code: def test_onset_strength_multi_ref():
      srand()
  
      # Make a random positive spectrum
      S = 1 + np.abs(np.random.randn(1025, 10))
  
      # Test with a null reference
      null_ref = np.zeros_like(S)
  
      onsets = librosa.onset.onset_strength_multi(
          S=S, ref=null_ref, aggregate=False, center=False
      )
  
      # since the reference is zero everywhere, S - ref = S
      # past the setup phase (first frame)
      assert np.allclose(onsets[:, 1:], S[:, 1:])
  
imports: import pytest
  from contextlib import nullcontext
  import os
  import warnings
  import numpy
  import librosa
  from test_core import srand
label_desc: Use image node_id 21 for calling a global function with example usage: test_onset_strength_multi_ref() without return types